U.S. patent number 8,329,585 [Application Number 12/620,335] was granted by the patent office on 2012-12-11 for method for reducing line width roughness with plasma pre-etch treatment on photoresist.
This patent grant is currently assigned to Lam Research Corporation. Invention is credited to Jonathan Kim, Ben-Li Sheu, Martin Shim.
United States Patent |
8,329,585 |
Sheu , et al. |
December 11, 2012 |
Method for reducing line width roughness with plasma pre-etch
treatment on photoresist
Abstract
A method for reducing line width roughness (LWR) of a feature in
an etch layer below a patterned photoresist mask having mask
features is provided. The method includes (a) non-etching plasma
pre-etch treatment of the photoresist mask, and (b) etching of a
feature in the etch layer through the pre-treated photoresist mask
using an etching gas. The non-etching plasma pre-etch treatment
includes (a1) providing a treatment gas containing H.sub.2 and COS,
(a2) forming a plasma from the treatment gas, and (a3) stopping the
treatment gas.
Inventors: |
Sheu; Ben-Li (Sunnyvale,
CA), Shim; Martin (Pleasanton, CA), Kim; Jonathan
(Danville, CA) |
Assignee: |
Lam Research Corporation
(Fremont, CA)
|
Family
ID: |
44011598 |
Appl.
No.: |
12/620,335 |
Filed: |
November 17, 2009 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20110117749 A1 |
May 19, 2011 |
|
Current U.S.
Class: |
438/689; 438/712;
438/706; 438/694; 216/41; 438/696; 216/67; 438/735 |
Current CPC
Class: |
H01L
21/0338 (20130101); H01J 37/32091 (20130101); H01J
37/32935 (20130101) |
Current International
Class: |
H01L
21/302 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
US. Appl. No. 12/595,234, filed Oct. 8, 2009. cited by other .
U.S. Appl. No. 12/263,662, filed Nov. 3, 2008. cited by other .
U.S. Appl. No. 12/233,517, filed Sep. 18, 2008. cited by
other.
|
Primary Examiner: Vinh; Lan
Assistant Examiner: Lu; Jiong-Ping
Attorney, Agent or Firm: Beyer Law Group LLP
Claims
What is claimed is:
1. A method for reducing line width roughness (LWR) of a feature in
an etch layer below a patterned photoresist mask formed of a
photoresist material and having mask features, the method
comprising: non-etching plasma pre-etch treatment of the
photoresist mask, comprising: providing a treatment gas containing
H.sub.2 and COS; forming a plasma from the treatment gas; stopping
the treatment gas; and etching a feature in the etch layer through
the pre-treated photoresist mask using an etching gas: wherein the
non-etching plasma pre-etch treatment does not open or
substantially etch the etch layer below the patterned photoresist
mask through the patterned photoresist mask, and wherein the
etching the feature in the etch layer through the pre-treated
photoresist mask reduces the LWR compared with etching of a feature
in the etch layer through the patterned photoresist mask without
performing the non-etching plasma pre-etch treatment of the
photoresist mask.
2. The method as recited in claim 1, wherein said non-etching
plasma pre-etch treatment further comprises: curing and smoothing
surfaces of the mask features using the plasma formed from the
treatment gas.
3. The method as recited in claim 2, wherein said curing and
smoothing includes: reducing single and double C--O bonds from the
surfaces of the photoresist mask using H.sub.2 component; and
depositing materials on sidewalls of the mask features using COS
component.
4. The method as recited in claim 3, wherein a thickness of the
deposited materials is less than 5 nm.
5. The method as recited in claim 1, wherein H.sub.2 and COS has at
least 50% of a total flow of the treatment gas.
6. The method as recited claim 4, wherein the treatment gas further
contains N.sub.2 and C.sub.4F.sub.8.
7. The method as recited claim 1, wherein the treatment gas
essentially consists of H.sub.2 and COS.
8. The method as recited claim 1, wherein a flow ratio of H.sub.2
and COS is about 10:1 to 60:1.
9. The method as recited claim 1, wherein a flow ratio of H.sub.2
and COS is about 20:1 to 50:1.
10. The method as recited claim 1, wherein said non-etching
pre-etch treatment includes: controlling a bias voltage such that
the non-etching plasma pre-etch treatment does not open or
substantially etch an underlying layer exposed through the mask
features.
11. The method as recited claim 1, wherein said forming the plasma
includes: applying a bias voltage between 0 to 500 V.
12. The method as recited claim 1, wherein said forming the plasma
includes: applying a bias voltage between 0 to 150 V.
13. The method as recited claim 1, wherein said non-etching
pre-treating substantially preserves an original aspect ratio of
the mask features.
14. A method for reducing line width roughness (LWR) of a feature
in an etch layer below a patterned photoresist mask formed of a
photoresist material and having mask features, the method
comprising: non-etching plasma pre-etch treatment of the
photoresist mask, comprising: providing a treatment gas containing
H.sub.2 and COS; forming a plasma from the treatment gas; stopping
the treatment gas; and etching a feature in the etch layer through
the pre-treated photoresist mask using an etching gas, wherein the
non-etching plasma pre-etch treatment does not open or
substantially etch the etch layer below the patterned photoresist
mask through the patterned photoresist mask, and further comprises:
curing and smoothing surfaces of the mask features using the plasma
formed from the treatment gas.
15. The method as recited in claim 14, wherein said curing and
smoothing includes: reducing single and double C--O bonds from the
surfaces of the photoresist mask using H.sub.2 component; and
depositing materials on sidewalls of the mask features using COS
component.
16. The method as recited in claim 15, wherein a thickness of the
deposited materials is less than 5 nm.
17. The method as recited claim 16, wherein the treatment gas
further contains N.sub.2 and C.sub.4F.sub.8.
18. The method as recited in claim 14, wherein H.sub.2 and COS has
at least 50% of a total flow of the treatment gas.
19. The method as recited claim 14, wherein the treatment gas
essentially consists of H.sub.2 and COS.
20. The method as recited claim 14, wherein said non-etching
pre-treating substantially preserves an original aspect ratio of
the mask features.
Description
BACKGROUND OF THE INVENTION
The present invention relates to reducing line width roughness
(LWR) of a feature of an etch layer. More specifically, the present
invention relates to a plasma pre-etch treatment of a patterned
photoresist mask through which a feature is to be etched in an
underlying etch layer.
During semiconductor wafer processing, features of the
semiconductor device are defined in the wafer using well-known
patterning and etching processes. In these processes
(photolithography), a photoresist (PR) material may be deposited on
the wafer and then is exposed to light filtered by a reticle. The
reticle may be a transparent plate that is patterned with exemplary
feature geometries that block light from propagating through the
reticle.
After passing through the reticle, the light contacts the surface
of the photoresist material. The light changes the chemical
composition of the photoresist material such that a developer can
remove a portion of the photoresist material, resulting in a
patterned photoresist mask. In the case of positive photoresist
materials, the exposed regions are removed, and in the case of
negative photoresist materials, the unexposed regions are removed.
Thereafter, the wafer is etched to remove the underlying material
from the areas that are no longer protected by the patterned
photoresist mask, and thereby produce the desired features in the
wafer.
As the critical dimensions (CDs) of semiconductor integrated
circuitry features shrinks below 45 nm, the control of photoresist
mask layers for line and space features with conventional
photolithography process is reaching its limits. Poor and distorted
line edges, as well as incompletely developed residue of
photoresist layer will cause significant roughness at the edges of
line and space features causing line edge roughness (LER) and
variation in the CD of the line and space features, i.e., line
width roughness (LWR). This non-uniform edge pattern will be
transferred and/or amplified during multiple etch process steps
that are required for semiconductor device fabrication, causing
degradation of device performance and yield loss.
The ideal feature has an edge that is "straight like a ruler" as
shown in FIG. 1A, when viewed from top down. However, for various
reasons as described above, the actual line feature may appear
jagged and have line width roughness (LWR). The LWR includes a
low-frequency roughness, such as a wiggling (as shown in FIG. 1B),
and a high-frequency roughness such as an irregular edge surface
(as shown in FIG. 1C). In reality, the LWR is a combination of the
high-frequency LWR and the low-frequency LWR. The LWR is a measure
of how smooth the edge of a linear feature is when viewed from the
top down. Features with high LWR are generally very undesirable
because the CD measured along the line feature would vary from
position to position, rendering operation of the resulting device
unreliable.
SUMMARY OF THE INVENTION
To achieve the foregoing and in accordance with the purpose of the
present invention, a method for reducing line width roughness (LWR)
of a feature in an etch layer below a patterned photoresist mask
having mask features is provided. The method includes (a)
non-etching plasma pre-etch treatment of the photoresist mask, and
(b) etching of a feature in the etch layer through the pre-treated
photoresist mask using an etching gas. The non-etching plasma
pre-etch treatment includes (a1) providing a treatment gas
containing H.sub.2 and COS, (a2) forming a plasma from the
treatment gas, and (a3) stopping the treatment gas.
The non-etching plasma pre-etch treatment may further include
curing and smoothing surfaces of the mask features using the plasma
formed from the treatment gas. The curing and smoothing may include
reducing single and double C--O bonds from the surfaces of the
photoresist mask using H.sub.2 component, and depositing materials
on sidewalls of the mask features using COS component. The
thickness of the deposited materials may be less than 5 nm. The
non-etching pre-treating substantially preserves an original aspect
ratio of the mask features.
In accordance with an embodiment of the present invention, H.sub.2
and COS has at least 50% of a total flow of the treatment gas.
Preferably, the H.sub.2 and COS has at least 60% of the total flow
of the treatment gas. More preferably, the H.sub.2 and COS has at
least 90% of the total flow of the treatment gas. The treatment gas
may further contain N.sub.2 and C.sub.4F.sub.8. In an embodiment of
the present invention, the treatment gas essentially consists of
H.sub.2 and COS. The flow ratio of H.sub.2 and COS may be between
10:1 to 60:1, preferably between 20:1 to 50:1, more preferably
about 30:1.
The non-etching pre-etch treatment may include controlling a bias
voltage such that the non-etching plasma pre-etch treatment does
not open or substantially etch an underlying layer exposed through
the mask features. The applied bias voltage may be between 0 to
500V, preferably between 0 to 150 V.
In another manifestation of the invention, an apparatus for
reducing line width roughness (LWR) of a feature in an etch layer
below a patterned photoresist mask having mask features is
provided. The apparatus comprises a plasma processing chamber that
includes a chamber wall forming a plasma processing chamber
enclosure, a substrate support for supporting a substrate within
the plasma processing chamber enclosure, a pressure regulator for
regulating the pressure in the plasma processing chamber enclosure,
at least one electrode for providing power to the plasma processing
chamber enclosure for sustaining a plasma, a gas inlet for
providing gas into the plasma processing chamber enclosure; and a
gas outlet for exhausting gas from the plasma processing chamber
enclosure. The plasma processing chamber further comprises a gas
source in fluid connection with the gas inlet. The gas source
includes a photoresist mask non-etching plasma pre-etch treatment
gas source, and a feature etching gas source. A controller is
controllably connected to the gas source and the at least one
electrode. The controller comprises at least one processor and
computer readable media. The computer readable media includes (a)
computer readable code for non-etching plasma pre-etch treatment of
the photoresist mask, including (a1) computer readable code for
providing a treatment gas containing H.sub.2 and COS, (a2) computer
readable code for forming a plasma from the treatment gas, and (a3)
computer readable code for stopping the treatment gas, and (b)
computer readable code for etching a feature in the etch layer
through the pre-treated photoresist mask using an etching gas.
In accordance with an embodiment of the present invention, the
computer readable code for non-etching plasma pre-etch treatment
further includes computer readable code for controlling a bias
voltage such that the non-etching plasma pre-etch treatment does
not open or substantially etch an underlying layer exposed through
the mask features.
The computer readable code for non-etching plasma pre-etch
treatment may further include computer readable code for
controlling a flow ratio of H.sub.2 and COS to be about 30:1.
These and other features of the present invention will be described
in more detail below in the detailed description of the invention
and in conjunction with the following figures.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated by way of example, and not by
way of limitation, in the figures of the accompanying drawings and
in which like reference numerals refer to similar elements and in
which:
FIGS. 1A-C are schematic diagrams for explaining line width
roughness.
FIG. 2 is a diagram illustrating a schematic cross-sectional view
of a stack of layers formed on a substrate, including a patterned
photoresist mask having mask features, processed in accordance with
one embodiment of the present invention.
FIG. 3 is a flow chart of a non-etching plasma pre-etch treatment
process in accordance with an embodiment of the invention.
FIGS. 4A and 4B schematically illustrate cross-sectional views of a
photoresist feature before and after a conventional H.sub.2-only
plasma pre-etch treatment, respectively.
FIGS. 4C and 4D schematically illustrate cross-sectional views of a
photoresist feature before and after the non-etching plasma
pre-etch treatment, respectively, in accordance with an embodiment
of the present invention.
FIG. 5 is a diagram illustrating a schematic view of a plasma
processing chamber that may be used for the non-etching plasma
pre-etch treatment in accordance with one embodiment of the present
invention.
FIGS. 6A and 6B schematically illustrate a computer system, which
is suitable for implementing a controller used in embodiments of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described in detail with
reference to a few preferred embodiments thereof as illustrated in
the accompanying drawings. In the following description, numerous
specific details are set forth in order to provide a thorough
understanding of the present invention. It will be apparent,
however, to one skilled in the art, that the present invention may
be practiced without some or all of these specific details. In
other instances, well known process steps and/or structures have
not been described in detail in order to not unnecessarily obscure
the present invention.
To facilitate understanding, FIG. 2 is a schematic cross-sectional
view of an example of a wafer stack 10 for front end of line (FEOL)
applications such as dielectric material etch in which embodiments
of the present invention may be applied. The wafer stack 10
includes a substrate 12 and a stack of layers 14 formed on the
substrate 12. As shown in FIG. 2, the stack of layers 14 includes
an etch layer 16 disposed below an antireflective coating (ARC)
layer 18 below a patterned photoresist (PR) mask 20 having mask
features. In this example, the photoresist mask 20 is of a 193 nm
or higher generation photoresist material, and has a line-space
pattern to form a plurality of lines and spaces in the etch layer.
For example, the mask features form a line-space pattern that
includes a plurality of lines where the mask material is formed,
and grooves between the lines where the mask material has been
removed by photolithography processes. The underlying layer, for
example, the ARC layer 18 is exposed through the mask pattern at
the bottom of the grooves. The PR mask 20 may have a CD about 45 nm
or less. The present invention is applicable for the FEOL
processes, such as a plasma pre-etch treatment of a photoresist
mask for memory mask open, as well as for dielectric material etch.
For example, the present invention is applied to a photoresist mask
for the 30 nm generation DRAM fabrication process.
As shown in FIG. 2, the etch layer 16 may include a dielectric
layer 22 and an amorphous carbon layer (ACL) 24 formed over the
dielectric layer 22. The ACL layer 24 may function as a hardmask.
The dielectric layer 22 may be made of a silicon oxide based
dielectric material such as SiO.sub.2, silicon nitride (SiN), or
tetora-ethyl-ortho-silicate (TEOS). Amorphous carbon is similar to
a polymer, but with less hydrogen and more carbon since it is
deposited at high temperature greater than 200.degree. C. by CVD,
and thus it is more etch resistant than polymer. The ARC layer 18
may include a bottom antireflective coating (BARC) layer 26 formed
below the PR mask 20, and a dielectric antireflective coating
(DARC) layer 28 below the BARC layer 26. These layers minimize or
eliminate reflections during exposure of the photoresist. The
BARC/DARC layers may be organic-based or inorganic-based, and are
usually composed of different materials from the underlying
dielectric material. For example, the BARC layer 26 may be made of
a carbon-based material, and the DARC layer 28 may be made of an
inorganic material such as silicon oxynitride (SiON). However, the
present invention is not limited to a specific stack of layers on
the substrate, but is applicable to any patterned photoresist mask
used as an etch mask for etching the underlying layers.
FIG. 3 is a process flow chart for a method that may be used in an
embodiment of the present invention. The method reduces line width
roughness of line and space features in the plasma etch process,
for example, for sub-45 nm node of dielectric etch applications. A
wafer stack with a patterned photoresist mask features is placed
into a plasma chamber (step 102), for example, a capacitively
coupled plasma reactor which is used to etch dielectric materials.
The plasma reactor may also be provided with conductor tools for
the subsequent conductor etch processes. The patterned photoresist
mask having mask features is treated (conditioned) by a non-etching
plasma pre-etch treatment process (step 104). The non-etching
plasma pre-etch treatment includes providing a treatment gas
containing H.sub.2 and COS (step 106), forming a plasma from the
treatment gas (step 108), with which the photoresist mask is
treated, and stopping the treatment gas (step 110) to stop the
non-etching pre-etch treatment. After the non-etching plasma
pre-etch treatment of the photoresist mask, the underlying etch
layer is etched through the pre-treated photoresist mask using
etching gases (step 112). It should be noted that the treatment gas
containing H.sub.2 and COS can also be used in inductively coupled
plasma reactors as long as similar bias and RF powers are
input.
For example, when the non-etching plasma pre-etch PR treatment is
applied to the wafer stack 14 as shown in FIG. 2, the subsequent
etch step 112 may include a BARC/DARC layer open process, a
hardmask (ACL) open process, and a dielectric etch process. It
should be noted that in the non-etching plasma pre-etch treatment
(step 104) does not open or substantially etch the underlying ARC
layer or other layer (second mask layer or dielectric layer)
exposed through the photoresist mask features. In other words, the
etch rate of the underlying layer is not detectable or very slow
and thus negligible.
In accordance with embodiments of the present invention, in the
non-etching plasma pre-etch treatment, the surfaces of the
photoresist mask features are cured and smoothed using the plasma
formed from the treatment gas. More specifically, the non-etching
plasma pre-etch treatment smoothens the edge of line-and-space
features, and strengthens the robustness of the photoresist from
shape deformation such as collapsing, twisting, wiggling, and the
like. Rough photoresist surfaces and edges developed during the
photolithography process are removed, such that undesirable excess
rough features at the line edges will not transfer to the final
etched features of the etch layer.
The use of hydrogen gas (H.sub.2) is believed to cure the
photoresist mask layer to provide a smoothened surface, as well as
to generate a surface with more uniform etch resistant. The curing
process by the H.sub.2 component in the plasma reduces single and
double C--O bonds from the surfaces of the photoresist mask (as a
chemical reaction), such that the cured photoresist mask will
sustain a more uniform edge deformation (i.e., less irregularities
in the line edges) during the subsequent etch processes, yielding a
better LWR. As a physical reaction, the photoresist mask shrinks as
a result of the cure process.
In accordance with the embodiments of the present invention, the
treatment gas further includes carbonyl sulfide (commonly written
as "COS", with the formula OCS) as an additive. The novel treatment
gas of the H.sub.2 and COS combination not only enhances
improvement in the LWR (especially high-frequency roughness)
compared with the conventional H.sub.2 only treatment gas (i.e.,
without COS), but also prevents the photoresist line patterns from
collapsing (low-frequency roughness or wiggling of the line
features). It is believed that the COS component in the non-etching
plasma pre-etch treatment facilitates depositing of materials on
sidewalls of the mask features using COS component. As a chemical
reaction, it is believed that the plasma from the COS component
creates bonds between sulfur and carbon on the surface of the
sidewalls. That is, the application of carbonyl sulfide in the
pre-etch plasma treatment facilitates passivation and strengthening
of the sidewalls of the photoresist features and reduce the line
pattern wiggling. In accordance with an embodiment of the present
invention, the thickness of the deposited materials is a few
nanometers, or less than 5 nm.
FIG. 4A schematically illustrates a cross-sectional view of a
line-pattern photoresist feature 30 and its aspect ratio (H/D).
Applicants has found that the curing process using a conventional
H.sub.2-only treatment gas is difficult to control its aggressive
attack to the sidewalls of the photoresist mask, and that the
process tends to thin down the photoresist mask feature 32 to have
a higher aspect ratio, as shown in FIG. 4B. Thinned line-pattern
features 32 and/or its higher aspect ratio due to curing may cause
a section of the line pattern to collapse, creating wiggling or
low-frequency LWR when viewed from the top.
FIG. 4C is a schematic yet more realistic cross-sectional view of a
photoresist feature 34. Typically, there is scum 36 such as residue
or undeveloped photoresist material at the bottom portion of the
mask features. Such undesirable residues also affect the LWR. In
accordance with the embodiments of the claimed invention, the novel
combination of H.sub.2 and COS as the treatment gas in the pre-etch
plasma treatment modifies (smoothes and strengthens) the surfaces
of the sidewalls of the photoresist features, and also maintains
the aspect ratio of the mask features. That is, the non-etching
plasma pre-treating substantially preserves the original aspect
ratio by passivating the sidewall of the photoresist mask features
by reaction with the COS component. Furthermore, it is believed
that oxygen radicals of the COS component also helps clean the scum
from the bottom portion of the mask features. FIG. 4D schematically
illustrates a photoresist feature 38 after the non-etching plasma
pre-etch treatment in accordance with an embodiment of the present
invention.
The embodiments of the claimed invention may be performed using a
capacitively coupled plasma reactor which is also used for the
subsequent dielectric material etching (i.e., in-situ process).
FIG. 5 shows a schematic view of a plasma processing chamber 300
that may be used for inventive non-etching plasma pre-etch
treatment. The plasma processing chamber 300 comprises confinement
rings 302, an upper electrode 304, a lower electrode 308, a gas
source 310, and an exhaust pump 320 connected to a gas outlet.
Within plasma processing chamber 300, a substrate 10 (a wafer with
the stack of layers) is positioned upon the lower electrode 308.
The lower electrode 308 incorporates a suitable substrate chucking
mechanism (e.g., electrostatic, mechanical clamping, or the like)
for holding the substrate 10. The reactor top 328 incorporates the
upper electrode 304 disposed immediately opposite the lower
electrode 308. The upper electrode 304, lower electrode 308, and
confinement rings 302 define the confined plasma volume 340. Gas is
supplied to the confined plasma volume 340 by the gas source 310
via a gas inlet 343, and is exhausted from the confined plasma
volume 340 through the confinement rings 302 and an exhaust port by
the exhaust pump 320. Besides helping to exhaust the gas, the
exhaust pump 320 helps to regulate pressure. In this embodiment,
the gas source 310 comprises a non-etching plasma pre-etch
treatment gas sources 330 including a H.sub.2 source 312 and a COS
source 314, and an optional additional gas source 316. The gas
source 310 may further comprise other gas sources, such as an
etching gas source 318 for the subsequent etch processes for the
etch layer to be performed in the processing chamber 300.
As shown in FIG. 5, an RF source 348 is electrically connected to
the lower electrode 308. Chamber walls 352 surround the confinement
rings 302, the upper electrode 304, and the lower electrode 308.
The RF source 348 may comprise a 60 MHz power source. The RF source
may also have a 2 MHz power source and a 27 MHz power source for
the subsequent etch processes. Different combinations of connecting
RF power to the electrode are possible. In the case of Lam Research
Corporation's Dielectric Etch Systems such as Exelan.RTM. Flex.TM.
Series, made by LAM Research Corporation.TM. of Fremont, Calif.,
which may be used in a preferred embodiment of the invention, the
27 MHz, 2 MHz, and 60 MHz power sources make up the RF power source
348 connected to the lower electrode, and the upper electrode is
grounded. A controller 335 is controllably connected to the RF
source 348, exhaust pump 320, and the gas source 310.
FIGS. 6A and 6B illustrate a computer system 400, which is suitable
for implementing a controller 335 used in embodiments of the
present invention. FIG. 6A shows one possible physical form of the
computer system. Of course, the computer system may have many
physical forms ranging from an integrated circuit, a printed
circuit board, and a small handheld device up to a huge super
computer. Computer system 400 includes a monitor 402, a display
404, a housing 406, a disk drive 408, a keyboard 410, and a mouse
412. Disk 414 is a computer-readable medium used to transfer data
to and from computer system 400.
FIG. 6B is an example of a block diagram for computer system 400.
Attached to system bus 420 are a wide variety of subsystems.
Processor(s) 422 (also referred to as central processing units, or
CPUs) are coupled to storage devices, including memory 424. Memory
424 includes random access memory (RAM) and read-only memory (ROM).
As is well known in the art, ROM acts to transfer data and
instructions uni-directionally to the CPU and RAM is used typically
to transfer data and instructions in a bi-directional manner. Both
of these types of memories may include any suitable of the
computer-readable media described below. A fixed disk 426 is also
coupled bi-directionally to CPU 422; it provides additional data
storage capacity and may also include any of the computer-readable
media described below. Fixed disk 426 may be used to store
programs, data, and the like and is typically a secondary storage
medium (such as a hard disk) that is slower than primary storage.
It will be appreciated that the information retained within fixed
disk 426 may, in appropriate cases, be incorporated in standard
fashion as virtual memory in memory 424. Removable disk 414 may
take the form of the computer-readable media described below.
CPU 422 is also coupled to a variety of input/output devices, such
as display 404, keyboard 410, mouse 412, and speakers 430. In
general, an input/output device may be any of: video displays,
track balls, mice, keyboards, microphones, touch-sensitive
displays, transducer card readers, magnetic or paper tape readers,
tablets, styluses, voice or handwriting recognizers, biometrics
readers, or other computers. CPU 422 optionally may be coupled to
another computer or telecommunications network using network
interface 440. With such a network interface, it is contemplated
that the CPU might receive information from the network, or might
output information to the network in the course of performing the
above-described method steps. Furthermore, method embodiments of
the present invention may execute solely upon CPU 422 or may
execute over a network such as the Internet in conjunction with a
remote CPU that shares a portion of the processing.
In addition, embodiments of the present invention further relate to
computer storage products with a computer-readable medium that have
computer code thereon for performing various computer-implemented
operations. The media and computer code may be those specially
designed and constructed for the purposes of the present invention,
or they may be of the kind well known and available to those having
skill in the computer software arts. Examples of tangible
computer-readable media include, but are not limited to: magnetic
media such as hard disks, floppy disks, and magnetic tape; optical
media such as CD-ROMs, DVDs, and holographic devices;
magneto-optical media such as floptical disks; and hardware devices
that are specially configured to store and execute program code,
such as application-specific integrated circuits (ASICs),
programmable logic devices (PLDs) and ROM and RAM devices. Examples
of computer code include machine code, such as produced by a
compiler, and files containing higher level code that are executed
by a computer using an interpreter. Computer readable media may
also be computer code transmitted by a computer data signal
embodied in a carrier wave and representing a sequence of
instructions that are executable by a processor.
Examples: In the non-etching plasma pre-etch treatment (step 104 as
described above), the treatment gas containing H.sub.2 and COS is
provided into the process chamber (confined plasma volume 340) from
the non-etching plasma pre-etch treatment gas source 330. The
treatment gas has a flow rate, and the H.sub.2 and COS has at least
50% of the total flow of the treatment gas. Preferably, the H.sub.2
and COS has at least 60% of the total flow of the treatment gas.
More preferably, the H.sub.2 and COS has at least 90% of the total
flow of the treatment gas. In an embodiment of the present
invention, the treatment gas essentially consists of H.sub.2 and
COS. Alternatively, the treatment gas may further contain N.sub.2
and C.sub.4F.sub.8, for example, up to 10% of the total flow of the
treatment gas. In accordance with an embodiment of the present
invention, the flow ratio of H.sub.2 and COS is between 10:1 to
60:1, preferably between 20:1 to 50:1, more preferably, about 30:1.
The treatment is formed into a plasma using a low bias, for
example, less than 500 volts. The bias voltage is controlled such
that the non-etching plasma pre-etch treatment does not open or
substantially etch an underlying layer exposed through the mask
features. Practically, the bias voltage for the low bias may be
between 100 to 150 volts. The flow of the treatment gas is stopped
to end the non-etching plasma pre-etch treatment.
A specific example of a treatment recipe provides a non-etching
plasma pre-etch treatment gas of 300 sccm H.sub.2 and 10 sccm COS
at a pressure of 15 mT. Ranges of the treatment gas in this example
recipe may provide 100-600 sccm H.sub.2 and 5 to 60 sccm COS, at
pressures between 2-150 mT, with preferred pressure below 80 mT.
Preferably, the ranges of the treatment gas in this example recipe
may provide 200-500 sccm H.sub.2 and 5 to 30 sccm COS, at pressures
between 2-40 mT. The power provided to form a plasma from the
treatment gas is 300-400 W at 60 MHz with a low bias voltage. More
specifically, the power is 400 W. The bias voltage is between 0 to
500 volts, preferably between 0 to 150 volts, more preferably
between 0 to 100 volts. That is, the non-etching plasma pre-etch
treatment is more chemical reaction than physical. An electrostatic
chuck temperature between -60.degree. C. and 200.degree. C. is
provided, while more desirable temperature is between -30.degree.
C. and 120.degree. C. The specific operating temperature for this
treatment is generally dependent upon the temperature required to
optimize the etch performance for subsequent layers of materials,
and this temperature should not be limited to the range described
above. The treatment process is maintained for 5-30 seconds,
preferably about 12 seconds. Longer treatment time may be performed
as needed to further improve LWR as long as there is enough PR
thickness left for subsequent etch after prescribed non-etching
plasma pre-etch treatment.
In accordance with embodiments of the present invention, the
high-frequency LWR (inspection length less than 75 nm) after the
non-etching plasma pre-etch treatment was about 3 nm or less, while
the high and low-frequency LWR (inspection length about 400 nm) was
about 4.5 nm or less. Compared with other additive gas, the novel
combination of H.sub.2 and COS is more effective for low frequency
LWR improvement, reducing wiggling of the line pattern.
While this invention has been described in terms of several
preferred embodiments, there are alterations, permutations,
modifications, and various substitute equivalents, which fall
within the scope of this invention. It should also be noted that
there are many alternative ways of implementing the methods and
apparatuses of the present invention. It is therefore intended that
the following appended claims be interpreted as including all such
alterations, permutations, and various substitute equivalents as
fall within the true spirit and scope of the present invention.
* * * * *